1. Field of the Invention
The present invention generally concerns ropes for elevators. In particular, the invention concerns a rope formed from high modulus synthetic fibers for use in elevator systems that employ traction sheaves to drive the rope and the elevator car connected to the rope. The ropes of the invention have an improved structure that reduces compression and abrasion deterioration over the life of the rope.
2. Description of Related Art
Conventional traction drive elevators employ an elevator car that is suspended by a rope in a hoistway. The rope typically extends upwardly to the top of the elevator shaft over a drive sheave and other sheaves and then back down the shaft to a counterweight. The drive sheave and the rope are in friction contact so that the rotation of the drive sheave displaces the rope and consequently raises or lowers the elevator car.
Prior art traction elevators have traditionally used steel wire ropes to drive the elevator. Steel ropes are relatively inexpensive and durable, but they are heavy. For high rise applications, the rope must be very long and the resulting weight of a steel rope must be offset with a compensating rope of similar weight (and a tensioning device) hanging from the underside of the car and counterweight. The combined weight of the car and rope often surpasses the tensile strength of the rope and consequently requires the use of additional ropes.
The prior art has developed a number of ropes from synthetic materials in an effort to replace steel ropes used in traction drive elevators. Examples of synthetic ropes are found in U.S. Pat. Nos. 6,508,051 to De Angelis, issued Jan. 21, 2003; 6,321,520 to De Angelis, issued Nov. 27, 2001; 6,318,504 to De Angelis, issued Nov. 20, 2001; 6,314,711 to De Angelis, issued Nov. 13, 2001; 6,164,053 to O'Donnell et al., issued Dec. 26, 2000; 5,881,843 to O'Donnell et al., issued Mar. 16, 1999; 5,834,942 to De Angelis, issued Nov. 10, 1998; 5,566,786 to De Angelis et al., issued Oct. 22, 1996; 5,651,245 to Damien, issued Jul. 29, 1997; 4,887,422 to Klees et al., issued Dec. 19, 1989; and 4,624,097 to Wilcox, issued Nov. 25, 1986.
The synthetic ropes developed thus far, however, have not adequately addressed the problems that arise from the use of synthetic materials. Synthetic ropes have at least two failure modes, namely compression and abrasion. The prior art synthetic ropes have attempted to address these two problems by constructing the ropes from a series of helically wound layers of fiber strands and placing intersheaths (typically constructed of polyurethane) between the layers. These attempts have not adequately solved the compression and abrasion problems that shorten the service life of the ropes. In addition, the use of intersheaths requires additional steps in the manufacturing process for such ropes and undesirably increases the elasticity of the rope, which can cause the elevator car to bounce as passengers enter and exit the car.
It would therefore be desirable to provide a light weight rope for elevators made from a synthetic material having improved resistance to compression and abrasion, and which removes the need for intersheaths in the construction of the rope.